Index: llvm/trunk/lib/Target/ARM/ARMInstrThumb.td
===================================================================
--- llvm/trunk/lib/Target/ARM/ARMInstrThumb.td
+++ llvm/trunk/lib/Target/ARM/ARMInstrThumb.td
@@ -592,6 +592,7 @@
                       [(ARMbrjt tGPR:$target, tjumptable:$jt)]>,
                       Sched<[WriteBrTbl]> {
     let Size = 2;
+    let isNotDuplicable = 1;
     list<Predicate> Predicates = [IsThumb, IsThumb1Only];
   }
 }
@@ -1471,7 +1472,7 @@
 // Thumb-1 doesn't have the TBB or TBH instructions, but we can synthesize them
 // and make use of the same compressed jump table format as Thumb-2.
 let Size = 2, isBranch = 1, isTerminator = 1, isBarrier = 1,
-    isIndirectBranch = 1 in {
+    isIndirectBranch = 1, isNotDuplicable = 1 in {
 def tTBB_JT : tPseudoInst<(outs),
         (ins tGPRwithpc:$base, tGPR:$index, i32imm:$jt, i32imm:$pclbl), 0,
          IIC_Br, []>, Sched<[WriteBr]>;
Index: llvm/trunk/test/CodeGen/Thumb/pr42760.ll
===================================================================
--- llvm/trunk/test/CodeGen/Thumb/pr42760.ll
+++ llvm/trunk/test/CodeGen/Thumb/pr42760.ll
@@ -0,0 +1,56 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=thumbv6m-none-unknown-eabi -tail-dup-placement-threshold=3 < %s | FileCheck %s
+
+define hidden void @test() {
+; CHECK-LABEL: test:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    movs r0, #1
+; CHECK-NEXT:    lsls r1, r0, #2
+; CHECK-NEXT:    b .LBB0_2
+; CHECK-NEXT:  .LBB0_1: @ %bb2
+; CHECK-NEXT:    @ in Loop: Header=BB0_2 Depth=1
+; CHECK-NEXT:    cmp r0, #0
+; CHECK-NEXT:    bne .LBB0_6
+; CHECK-NEXT:  .LBB0_2: @ %switch
+; CHECK-NEXT:    @ =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    adr r2, .LJTI0_0
+; CHECK-NEXT:    ldr r2, [r2, r1]
+; CHECK-NEXT:    mov pc, r2
+; CHECK-NEXT:  @ %bb.3:
+; CHECK-NEXT:    .p2align 2
+; CHECK-NEXT:  .LJTI0_0:
+; CHECK-NEXT:    .long .LBB0_6+1
+; CHECK-NEXT:    .long .LBB0_4+1
+; CHECK-NEXT:    .long .LBB0_6+1
+; CHECK-NEXT:    .long .LBB0_5+1
+; CHECK-NEXT:  .LBB0_4: @ %switch
+; CHECK-NEXT:    @ in Loop: Header=BB0_2 Depth=1
+; CHECK-NEXT:    b .LBB0_1
+; CHECK-NEXT:  .LBB0_5: @ %bb
+; CHECK-NEXT:    @ in Loop: Header=BB0_2 Depth=1
+; CHECK-NEXT:    cmp r0, #0
+; CHECK-NEXT:    beq .LBB0_1
+; CHECK-NEXT:  .LBB0_6: @ %dead
+entry:
+  br label %switch
+
+switch:                                           ; preds = %bb2, %entry
+  switch i32 undef, label %dead2 [
+    i32 0, label %dead
+    i32 1, label %bb2
+    i32 2, label %dead
+    i32 3, label %bb
+  ]
+
+dead:                                             ; preds = %bb2, %bb, %switch, %switch
+  unreachable
+
+dead2:                                            ; preds = %switch
+  unreachable
+
+bb:                                               ; preds = %switch
+  br i1 undef, label %dead, label %bb2
+
+bb2:                                              ; preds = %bb, %switch
+  br i1 undef, label %dead, label %switch
+}